To secure the enclosure of safes and vaults, a combination lock is attached to the door of the enclosure. Some vaults and safes are small enough to be elevated and dropped, which could cause some of the elements of the lock mechanism to realign or shift position. At least momentarily, the parts of the lock mechanism would be in a position to allow the opening of the lock, not withstanding the fact that it has not been unlocked by dialing. If the dial is operated at the moment the elements are so positioned, the lock may be opened.
In electronic combination locks, when the lock is in the locked condition the connection between the dial shaft, that the dial rotates, and the bolt is normally disengaged. The rotation of the dial shaft will not cause any of the bolt withdrawal linkage to move due to the disengagement.
Unless interlocked, the bolt withdrawal linkage is subject to being displaced to a position in that the wheel may be turned and the bolt withdrawn. If this is possible, the lock could be opened in the sense of the bolt being withdrawn, even though the proper combination has not been entered. This may be possible if the lock and the enclosure are impacted in the correct direction with a force sufficient to cause the inertia of the pawl to cause the pawl to move into an engagement zone with the wheel and the wheel is quickly turned after the impact to catch and pull the pawl to withdraw the bolt into the lock housing.
Under normal lock operations as the connection of the wheel to the pawl is controlled by a very small stepper motor or similar low current, low voltage device being actuated, thus a large mass interlock is not practical. The stepper motor rotates a gear into engagement so that a larger force may be used to move the chain of parts to accomplish the engagement of the pawl with the wheel.